Wireless devices go battery-free with new communication technique

August 13, 2013
by Michelle Ma

Using ambient backscatter, these devices can interact with users and communicate with each other without using batteries. They exchange information by reflecting or absorbing pre-existing radio signals. Credit: University of Washington

(Phys.org) —We might be one step closer to an Internet-of-things reality. University of Washington engineers have created a new wireless communication system that allows devices to interact with each other without relying on batteries or wires for power.

The new communication technique, which the researchers call "ambient backscatter," takes advantage of the TV and cellular transmissions that already surround us around the clock. Two devices communicate with each other by reflecting the existing signals to exchange information. The researchers built small, battery-free devices with antennas that can detect, harness and reflect a TV signal, which then is picked up by other similar devices.

"We can repurpose wireless signals that are already around us into both a source of power and a communication medium," said lead researcher Shyam Gollakota, a UW assistant professor of computer science and engineering. "It's hopefully going to have applications in a number of areas including wearable computing, smart homes and self-sustaining sensor networks."

Everyday objects could be enabled with battery-free tags to communicate with each other. A couch could use ambient backscatter to let the user know where his keys were left. Credit: University of Washington

The researchers published their results at the Association for Computing Machinery's Special Interest Group on Data Communication 2013 conference in Hong Kong, which begins Aug. 13. They have received the conference's best-paper award for their research.

"Our devices form a network out of thin air," said co-author Joshua Smith, a UW associate professor of computer science and engineering and of electrical engineering. "You can reflect these signals slightly to create a Morse code of communication between battery-free devices."

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Smart sensors could be built and placed permanently inside nearly any structure, then set to communicate with each other. For example, sensors placed in a bridge could monitor the health of the concrete and steel, then send an alert if one of the sensors picks up a hairline crack. The technology can also be used for communication – text messages and emails, for example – in wearable devices, without requiring battery consumption.

The researchers tested the ambient backscatter technique with credit card-sized prototype devices placed within several feet of each other. For each device the researchers built antennas into ordinary circuit boards that flash an LED light when receiving a communication signal from another device.

Researchers demonstrate how one payment card can transfer funds to another card by leveraging the existing wireless signals around them. Ambient RF signals are both the power source and the communication medium. Credit: University of Washington

Groups of the devices were tested in a variety of settings in the Seattle area, including inside an apartment building, on a street corner and on the top level of a parking garage. These locations ranged from less than half a mile away from a TV tower to about 6.5 miles away.

They found that the devices were able to communicate with each other, even the ones farthest from a TV tower. The receiving devices picked up a signal from their transmitting counterparts at a rate of 1 kilobit per second when up to 2.5 feet apart outdoors and 1.5 feet apart indoors. This is enough to send information such as a sensor reading, text messages and contact information.

It's also feasible to build this technology into devices that do rely on batteries, such as smartphones. It could be configured so that when the battery dies, the phone could still send text messages by leveraging power from an ambient TV signal.

The applications are endless, the researchers say, and they plan to continue advancing the capacity and range of the ambient backscatter communication network.

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27 comments

I was wondering when this was coming. Most people don't know a version of this for almost a decade is how auto radio audience size is estimated by setting up devices at freeways and counting how many cars are listening to what radio stations.

They found that the devices were able to communicate with each other, even the ones farthest from a TV tower. The receiving devices picked up a signal from their transmitting counterparts at a rate of 1 kilobit per second when up to 2.5 feet apart outdoors and 1.5 feet apart indoors. This is enough to send information such as a sensor reading, text messages and contact information.It's also feasible to build this technology into devices that do rely on batteries, such as smartphones. It could be configured so that when the battery dies, the phone could still send text messages by leveraging power from an ambient TV signal.

Believe it or not, that nowadays even we know that they communicate with each other by radio wave, but we still do not understand how the wave could propagate via vacuum space without using any medium? Maybe there is something wrong with the conventionally explanation….http://www.vacuum...20〈=en

If these devices have to be so close to each other to communicate, why not just use wires? They could still use the TV signal as a power source, and the units could be farther apart. There would also be no confusion as to which of the near by sensors was sending out which data.

Principal sensor in the Brain....Info about Each & Every object kept in the house should be propagated finally to the Brain.Then, we can beat the computer that records everything for storage until we deliberately Erase it!This idea is the starting point for something great to come in the coming decades.It is true Researchers may waste physical & human resources if funding is plenty. At the same time I think the Govt. should aggressively fund & support topmost ideas. It is useless to rely on Private Sector alone which is purely motivated by Profits to survive. Just because Manufacturing causes pollution....it should not mean that we have to buy each & every object made elsewhere. Just because it is cheap...it should not deprive jobs here...Private Sector is Ruthless. It creates Wars in Other Nations to SELL Arms & Ammunition there. RIDICULOUS indeed.

Read what Jeff Greenfield writes here: "As a child of the 1950s, I was certain of the wonders in store when I became an adult. We'd fly to Europe in an hour; we'd vacation on the moon; we'd commute to work in personal aircraft or jetpacks or helicopters. The same transit breakthroughs that had transformed the world of my parents' and grandparents' would transform mine, too.

And then, somewhere around the start of the 1970s, that future ground to a halt — and nowhere more so (at least in the First World) than in the nation where technological innovation was part of its DNA."http://news.yahoo...641.html

Can probably calculate the frequency they use. The antenna has to have at least half the wavlength.From the images the antenna looks to be about 20cm.

What types of frequencies they use to communicate is a different matter. But as this is so very low power/short range I wouldn't worry too much about these devices interfering with any other signal (other than maybe in a hospital setting, where EMC guidelines are rather more stringent)

The retransmission is at very low power (and it is retransmitting signals which would be lost in any case). You're not degrading any signal, here (unless you put a lot of these devices in line of sight between you and your TV antenna).

The information by the device is modulated on top of the retransmitted/reflected signal at a much higher frequency. So even if you wanted to catch the signal for its original purpose (e.g. to watch TV) you wouldn't notice, as your TV receiver does not decode at those frequency ranges.

The antenna length is determined by the wavelength of the radiation you want to capture.Fractal antenna are applicable to a different problem. They maximise the number of (very small) antennas per surface/volume (2D/3D, to maximise the energy transmitted/received per surface/volume). But here you only need a linear antenna (1D), so a fractal antenna isn't useful (there is no such thing as a fractal with 1 (or less) dimensions. At least not one you could use as an antenna).

So many possibilities that I am focusing on. Pooku madda matladukodamu...Denguladukodaniki mundu....See how difficult it is even to understand words made of English Letters!

When someone gave me this puzzle, I was nonplussed in the beginning.Luckily, Intelligent Google (Search) which has been a pioneer after Microsoft came to the rescue....at least to make an outline of it!

Well i get that they modulate the scattering of another signal to transmit information without any additional RF power, like blocking and exposing an existing light source can transmit morse code but any circuitry that forms and decodes messages must have a power source.The article did not specify but if the boards are truly wireless then they must be capturing enough RF energy to power the circuitry and I think this would be very difficult to do. RF energy simply isn't that dense in most locations.

Next is the issue that modulating backscatter will interfere with devices using the spectrum nearby. Engineers go to substantial lengths to design RF demodulators for such problems as are caused by moving multiple reflections.

Principal sensor in the Brain....Info about Each & Every object kept in the house should be propagated finally to the Brain.Then, we can beat the computer that records everything for storage until we deliberately Erase it!This idea is the starting point for something great to come in the coming decades.It is true Researchers may waste physical & human resources if funding is plenty. At the same time I think the Govt. should aggressively fund & support topmost ideas. It is useless to rely on Private Sector alone which is purely motivated by Profits to survive. Just because Manufacturing causes pollution....it should not mean that we have to buy each & every object made elsewhere. Just because it is cheap...it should not deprive jobs here...Private Sector is Ruthless. It creates Wars in Other Nations to SELL Arms & Ammunition there. RIDICULOUS indeed.

Further input to condemn/appreciate on UBathtub Sri M R Venkatesh on "American Debt Cisis - Lessons for the World"

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